WebGLRenderer: Clean up.

src/renderers/WebGLRenderer.js

@@ -1767,7 +1767,7 @@ function WebGLRenderer( parameters ) {
 
 	};
 
-	this.setRenderTarget = function ( renderTarget, activeCubeFace, activeMipmapLevel ) {
+	this.setRenderTarget = function ( renderTarget, activeCubeFace = 0, activeMipmapLevel = 0 ) {
 
 		_currentRenderTarget = renderTarget;
 		_currentActiveCubeFace = activeCubeFace;
@@ -1788,7 +1788,7 @@ function WebGLRenderer( parameters ) {
 
 			if ( renderTarget.isWebGLCubeRenderTarget ) {
 
-				framebuffer = __webglFramebuffer[ activeCubeFace || 0 ];
+				framebuffer = __webglFramebuffer[ activeCubeFace ];
 				isCube = true;
 
 			} else if ( renderTarget.isWebGLMultisampleRenderTarget ) {
@@ -1827,7 +1827,7 @@ function WebGLRenderer( parameters ) {
 		if ( isCube ) {
 
 			const textureProperties = properties.get( renderTarget.texture );
-			_gl.framebufferTexture2D( _gl.FRAMEBUFFER, _gl.COLOR_ATTACHMENT0, _gl.TEXTURE_CUBE_MAP_POSITIVE_X + ( activeCubeFace || 0 ), textureProperties.__webglTexture, activeMipmapLevel || 0 );
+			_gl.framebufferTexture2D( _gl.FRAMEBUFFER, _gl.COLOR_ATTACHMENT0, _gl.TEXTURE_CUBE_MAP_POSITIVE_X + activeCubeFace, textureProperties.__webglTexture, activeMipmapLevel );
 
 		}